The present application relates to an electrode that includes a lithium composite oxide, to a secondary battery that uses the electrode, to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and to an electronic apparatus that use the secondary battery.
In recent years, various electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been strongly demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long life. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed. In these days, it has been considered to apply such a secondary battery to various other applications represented by a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, or an electric power tool such as an electric drill.
As the secondary battery, secondary batteries that obtain a battery capacity by utilizing various charge and discharge principles have been proposed. Specially, a secondary battery utilizing insertion and extraction of lithium ions or the like as an electrode reactant is considered promising, since such a secondary battery provides higher energy density than lead batteries, nickel cadmium batteries, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The cathode has a cathode active material layer on a cathode current collector. The cathode active material layer contains a cathode active material contributing to a charge and discharge reaction. As the cathode active material, generally, a lithium composite oxide such as LiCoO2, LiNiO2, and LiMn2O4, or a lithium phosphate compound such as LiFePO4 is used.
A composition of the cathode active material largely affects performance of the secondary battery. Therefore, various studies have been made on the composition of the cathode active material. Specifically, to obtain superior charge and discharge characteristics and the like, Zr is added to Li1-xCoO2 (0≦x<1) (for example, see Japanese Patent No. 0285877). To improve cycle characteristics under a high voltage, LixCo1-y-zZryMezO2-a (Me represents elements such as a metal element with atomic number of 11 or more other than Co and Zr, 1<x<1.2, 0<y≦0.01, 0≦z<0.1, and −0.1≦a≦0.1) containing Zr as a constituent element is used (for example, see Japanese Unexamined Patent Application Publication No. 2002-358963). To suppress performance deterioration at the time of storing a battery, an oxide of a heterogeneous element such as Zr is mixed in a lithium transition metal composite oxide such as lithium manganate (for example, see Japanese Unexamined Patent Application Publication No. 2006-066330). To obtain a high charge and discharge capacity even if the charge final voltage is equal to or higher than 4.3 V, a compound containing Zr is sintered in a state of particles on the surface of LiCoO2 (for example, see Japanese Patent No. 4307962). To obtain superior load characteristics and superior cycle characteristics, LiCoO2 particle powder is covered with a Zr compound to localize a zirconium compound on the surface of the LiCoO2 particle powder (for example, see Japanese Unexamined Patent Application Publication No. 2008-311132). To obtain superior charge and discharge characteristics and superior large current charge and discharge characteristics, P is added to one or more selected from the group consisting of LiMn2O4, LiCoO2 and LiNiO2 (for example, see Japanese Unexamined Patent Application Publication No. H05-036411). To retain a high operating voltage and obtain superior charge and discharge characteristics, a lithium compound, a cobalt compound, and phosphoric acid are mixed, heat treatment is subsequently performed on the mixture in an oxidant atmosphere, and particle surfaces of the resultant Li—Co composite oxide are covered with P (for example, see Japanese Patent No. 3054829). To improve cycle characteristics under high temperature, a mixture of LixMO2 (M represents at least Mn, and 0.01≦x≦1.5) and a phosphorous compound is used (for example, see Japanese Unexamined Patent Application Publication No. H10-241681). To improve cycle characteristics, low temperature heavy load characteristics, and safety, a zirconium-containing lithium-cobalt composite oxide and LixCo1-yAyO2 (A represents Mg or the like, 0.05≦x≦1.15, and 0≦y≦0.03) are mixed in LitCoMsO2 (M represents Fe or the like, 0≦s≦0.03, and 0.05≦t≦1.15) (for example, see Japanese Unexamined Patent Application Publication No. 2007-214090).